If it is not obvious why a postscript file is so big, try viewing it with a postscript viewer. As the file is displayed, you will see which parts take a long time to draw: these are the likely sources of the problem.
If the file is drawn quite quickly, but takes a long time to start, it is likely that there are a lot of font definitions which have been included in the postscript. In this case the postscript should be re-generated without any fonts included.
Again it is useful to review the postscript with a viewer. If there is nothing obvious, the problem is probably coming from a file containing an illustration. Try re-making the postscript with other options or use a different printer driver.